1. Field of the Invention
The present invention generally relates to a swash plate type refrigerant compressor and, more particularly, to a lubricating mechanism between the shoe and swash plate.
2. Description of the Prior Art
A swash plate type refrigerant compressor suitable for use in an automotive air condition system is disclosed in, for example, U.S. Pat. No. 4,568,252 to Ikeda et al. The Ikeda et al. swash plate compressor includes a pair of axially aligned front and rear cylinder blocks enclosed at both ends by front and rear housings. Valve plates are positioned between the respective cylinder blocks and the front and rear housings. The front and rear housings form suction chambers and discharge chambers, and a plurality of aligned cylinder bores are arranged around the central axis of the cylinder blocks. Each of the cylinder bores have interconnecting suction chambers and discharge chambers formed in the front and rear housings. The cylinder blocks also have a central longitudinal bore formed therein. A drive shaft is rotatably mounted in the longitudinal bores. A swash plate chamber is formed between the cylinder blocks and a swash plate, keyed on the drive shaft, is rotatably received is the swash plate chamber.
The swash plate rotates with the drive shaft and operatively engages double-headed pistons slidably fitted in the cylinder bores. More specifically, the swash plate is coupled to the pistons through shoes. The shoes provide a universal coupling allowing a reciprocatory compressing motion of the pistons within the cylinder bores in response to the rotation of the swash plate. The central portion of each of the double headed pistons is provided with a recess through which the swash plate passes during the rotation thereof, and a pair of spherical sockets to receive the shoes. Each of the shoes has a circular flat face in sliding contact with the oblique face of the swash plate and a half-spherical face in sliding engagement with the socket of the associated piston.
When the Ikeda et al. compressor is used for compressing a refrigerant gas in the air-conditioning system of a vehicle, the refrigerant gas, which contains a lubricating oil, is introduced from outside of the air-conditioning circuit into the suction chamber, via the swash plate chamber, and is discharged from the compressor to other components in the air-conditioning circuit. The lubricating oil contained in the refrigerant gas lubricates the contacting surfaces of the shoes and the swash plate and respective sockets of the pistons. However, since the circular flat surface of each shoe and the oblique surface of the swash plate are in close contact, sometimes an insufficient amount of lubricating oil is supplied to the contacting surfaces of the shoes and the swash plate. Moreover, since the lubricating oil entering the swash plate chamber is subjected to the centrifugal force of the rotating swash plate and is scattered radially outward from the swash plate, the lubricating oil is not retained between the shoes and the swash plate. Consequently, the engaging surfaces between the shoes and the double headed pistons and the swash plate are sometimes insufficiently lubricated.
This lack of lubrication is even more pronounced when the engagement between the shoes and the pistons is located remotely from the return gas inlet through which the refrigerant gas is introduced into the swash plate chamber. As a result, abrasion between the swash plate and the flat surfaces of the shoes can occur during the operation of the swash plate type compressor due to an insufficient or a lack of lubrication. This can cause inaccurate reciprocation by the double headed pistons, i.e., lost motion of the pistons due to play between the pistons and the shoes, and noise during the operation of the compressor. Further, in an extreme case, the insufficient or lack of lubrication can cause excessive frictional contact between the oblique face of the swash plate and the flat faces of the respective shoes, resulting in the generation of high temperatures, which can cause the contacting faces of the swash plate and shoes to seize.